The invention relates to a method for improving soil and/or for lifting ground-based structures, the method comprising providing the soil or structure with a hole, arranging into the hole an injection bar and an expansion element provided in connection therewith, and injecting a substance into the expansion element.
The invention further relates to an arrangement for improving soil and/or for lifting structures, the arrangement comprising an injection bar to be arranged into a hole and provided in connection with an expansion element, a substance to be injected into the expansion element, and means for injecting the substance into the expansion element.
Soil is improved e.g. in order to increase the bearing capacity thereof or in order to fill empty spaces therein. Further, soil improvement is necessary if vibrations transmitted via the soil are to be dampened or soil liquefaction taking place in connection with earthquakes is to be prevented. A process of lifting structures, in turn, refers e.g. to lifting and stabilizing buildings or foundations for buildings or floors that are damaged, subsided or dislocated. Furthermore, the process of lifting structures comprises lifting and stabilizing subsided paved roads or fields, such as concrete and asphalt roads or runways.
Deterioration of soil or subsidence of structures may be caused e.g. by poorly consolidated soil, water-induced erosion, inappropriate soil type during construction, deterioration of frictional forces in the soil, or variations in temperature or humidity conditions. Further, soil deterioration may be caused by changes in conditions due to mechanical damage, such as breakage of water or sewer pipes. Moreover, soil conditions may change due to the influence of dynamic forces.
In order to improve the soil, soil having a poor bearing capacity is replaced by a substance having a better bearing capacity. Such a process called mass exchange is extremely laborious and expensive. Further, piling techniques, such as friction piles which, through friction, are supported by the soil, or base piles which rest on the hard bottom layer, are used. Piling requires heavy and complex equipment, which subjects the environment to noise and further disturbance. Since the piling is fastened to a structure, it subjects the structure to point loads when the structure is supported by piles, and not by the soil.
EP 0 851 064 discloses a solution for improving the bearing capacity of soil. In the solution, the soil is provided with holes into which a substance which expands as a consequence of a chemical reaction is injected. EP 1 314 824 discloses a similar solution wherein a substance is used for producing a pressure of more than 500 kPa. In practice, it has been noticed that in these solutions, the only way to determine a dose to be injected is to monitor the surface of the ground or the height level of a building, and stop injecting when a reaction in these aspects is observed. When these solutions are used in connection with porous and soft soils in particular, the procedures of dosing the substance to be injected appropriately and directing the expansion force correctly as well as keeping the substance in a desired place present very challenging tasks.
JP 7 018 651 discloses a solution wherein expanding bag bodies are arranged into holes drilled into the soil. A hardening agent is pumped into the bags with a high pressure. Due to the usage of a high hydraulic pressure, the devices used are complex and, for example, valves that are failure-sensitive in difficult conditions are required. Furthermore, in soft soil, it is uncertain that the bag stays in place, so it is very difficult to condense a portion of soft soil by means of this solution. Still further, if a bag is broken, the condensing process gets totally out of control. JP 10 195 860 discloses a similar solution wherein a flexible bag is used. This solution also suffers from problems similar to those disclosed above. JP 2003 105 745 discloses a solution wherein plastic mortar is injected into soil or into a bag arranged in the soil. The above-disclosed problems are present also in this solution when a substance is injected into a bag.
JP 9 158 235 discloses a solution for correcting inclination of a building. The solution comprises drilling a hole which extends under the foundations of the building. Here, under the foundations, a flexible bag is arranged into which water and a consolidating substance are conveyed through separate pipes. The aim is to lift the building through filling the bag. This solution also requires the usage of an extremely high hydraulic pressure, resulting in complex and failure-sensitive equipment. The equipment also includes a plurality of pipes, which adds to its complexity. Furthermore, if a bag is broken while in use, the structure may collapse at the particular bag, so the method is extremely risky.